1. Technical Field
The present invention generally relates to methods of wear testing tires and, more particularly, to a method for defining a tire load history that is used in an indoor wear test. Specifically, the present invention relates to a method of defining a tire load history and using the tire load history to conduct an indoor wear test on the tire.
2. Background Information
Automobile and tire manufacturers desire wear testing to be performed on tires. Different methods of wear testing tires are known in the art. In one known method, the test tires are placed on a vehicle that will be frequently driven. The tires are measured after the vehicle is driven a selected number of miles. Another known test procedure is performed indoor on a wear test drum. A wear test drum provides a rotating surface that engages the tire to simulate a road surface. The wear test drum provides mechanisms for varying the force between the tire and the rotating surface. The velocity of the rotating surface may also be varied. The user may simulate actual public road driving conditions by varying these forces and the velocity. The problem in the prior art is that the user cannot easily determine what forces and velocities to use to simulate public road driving conditions for a specific vehicle.
For instance, one may wish to simulate tire wear with a specific tire on a specific vehicle over a daily commute that includes country road, highway, and city road driving conditions. The total length of the daily commute over a one year period may be 15,000 miles. The forces between the tire and the road constantly change through this commute and the person conducting the indoor wear test desires to accurately simulate these forces on the test tire with the indoor test drum.
One method of predicting the tire forces is to instrument a test vehicle with wheel force transducers that are mounted as part of the wheel and rotate with the wheel/tire assembly while the vehicle is driven over a controlled test track. The vehicle is equipped with a data acquisition system that stores signals from the transducers. For instance, front and rear radial force, lateral force, drive/brake force, and tire velocities may be recorded. A problem with this measurement system is that the equipment is difficult to transport from test location to test location, the setup time is long, and the vehicle cannot be driven on public roads while equipped with the transducers. The data is thus only gathered on a test track that simulates public road driving conditions. The process of gathering the force histories for a given car with a given tire is expensive and often consumes weeks of time. The process must be repeated for different cars and for different tires. The art thus desires a faster and easier method of generating tire loading histories for indoor wear tests. The art also desires that the method for generating the tire loading histories result in more accurate load histories for the test machine.
The present invention provides a method for determining tire load histories for use with an indoor wear test machine. In one embodiment of the invention, sample tire forces are measured with a vehicle test system. The data from the test system is used to create formulas that relate the tire forces to the accelerations experienced by the vehicle. In another embodiment of the invention, a computer model of the vehicle may be used to conduct a set of basic maneuvers to provide the data to create the formulas that relate the tire forces to the accelerations experienced by the vehicle.
An instrumented vehicle driven over a wear test course records data which is used to generate a xe2x80x9csignaturexe2x80x9d for that course. This data is used with the formulas to create the input forces for an indoor wear test machine. In one embodiment of the invention, the data is gathered at a fixed distance interval rather than a fixed time interval.
The invention also provides a method of translating the data gathered from the outdoor test vehicle into tire load data that may be used to operate an indoor tire wear test drum to perform an indoor tire wear test.